Brushless direct current motors, also referred to as electronically-commutated motors, are often used in HVAC systems due to the high efficiency, long life, and ease of controlling speed, torque, and airflow. Such motors are generally synchronous motors powered by a direct current electric source and associated switching power supply to produce a switching (bi-directional) current.
The maximum power that can be applied to a brushless motor is generally limited by heat generated in the motor. Too much heat can cause damage to winding insulation within the motor. Brushless motors are traditionally higher cost than brushed direct current motors. For example, brushless motors generally require use of an electronic speed controller to operate. Furthermore, even brushed direct current motors may require a similar controller if variable speed control is desirable. Furthermore, the electronic speed controller is generally designed to receive a particular type of input signal, such as a constant direct current voltage signal of a particular value, or an alternating current signal. Such controllers generally lack flexibility to operate with other types of inputs, for example because a specific type of motor expects a certain type of signal. As such, design of systems interfacing to those HVAC controllers is constricted.
Manufacturers of HVAC systems desire to operate motors at a cost minimum, but at the same time, wish to take advantage of the above-cited advantages of brushless direct current motors. Manufacturer of such systems also want to limit the number of different types of motors used, by programming those motors for use in multiple design configurations.
For these and other reasons, improvements in control circuits associated with brushless direct current motors, in particular those used in connection with HVAC systems, are desirable.